PUB, the national water agency, is embarking on new drainage improvement projects at 36 locations, adding to its on-going drainage projects at 176 locations around Singapore.
These drainage improvement projects are part of a "source-pathway-receptor" strategy to improve flood protection for Singapore, said PUB on Monday.
Besides "pathway" solutions, PUB will also implement a "source" measure - the construction of the Stamford Detention Tank, which is scheduled to start by end of this year.
Sited near the junction of Tyersall Avenue and Tyersall Road, the detention tank will help to reduce the peak flow of stormwater into the public drains and better protect the Stamford Canal catchment against floods during intense storms. With a storage capacity of about 38,000 cubic metres or 15 Olympic-sized pools, the Stamford Detention Tank will be built underground. Occupying a subterranean footprint of about 0.5 hectares, the tank will be sited directly beneath a nursery and a coach bay of the upcoming Singapore Botanic Gardens' Learning Forest extension.
Once completed in 2016, the detention tank will be able to temporarily hold excess stormwater from the drains along Holland Road, which is the upstream area of the Stamford Canal catchment. After the rain subsides, the water will be pumped back into the drains for subsequent discharge into the Marina Reservoir.
Besides the detention tank, PUB will be constructing the Stamford Diversion Canal which will divert stormwater from the upstream section of the Stamford Canal catchment to the Singapore River. The work will be carried out in phases, with two tenders to be called. The first tender will be called in the fourth quarter of 2013 and the other tender will be called in the first quarter of 2014. Work on the entire diversion canal is expected to be completed by 2017.
Under the long-term drainage upgrading of Sungei Pandan Kechil, PUB will be carrying out the detailed design in 2014, followed by the widening and deepening of the canal in 2015. In the interim, PUB has enlarged the inlet and outlet points of the culvert crossing at AYE 9.6km to improve the flow of water. The agency will also be calling a tender for the construction of a tidal gate in November this year.
Other drainage upgrading works at Alexandra Canal Subsidiary Drain "F" (between Tiong Bahru Road to Havelock Road) and Siglap Canal (between ECP to the sea) will also start in the second and third quarter of 2014 respectively.
Drainage improvement projects at 176 locations are also on-going across the island. These include works at major canals or outlet drains like Bukit Timah 1st Diversion Canal, Rochor Canal, Alexandra Canal, and Sin Ming Outlet drain / Marymount Rd Culvert.
In the last two years, PUB has completed drainage improvement projects at 90 locations. Some of these completed projects include works at Geylang River from Guillemard to Dunman Road, Bukit Timah Canal from Maple Avenue to Kampong Chantek, and upgrading of roadside drains across the island such as at Meyer Rd and Sunset Drive/Way.
One of the measures PUB is adopting to prepare for the upcoming Northeast Monsoon season and to minimise the risks of flash floods is to work together with the National Environment Agency's Department of Public Cleanliness (DPC) to step up efforts in drainage maintenance and monitoring to keep the drains free flowing.
At the same time, PUB has intensified inspections at some 100 construction worksites around the island to check for obstructions in the drains. As part of the day-to-day operations, PUB continues to work closely with other agencies like LTA, NParks, NEA and Town Councils to ensure that drainage systems are functioning effectively.
PUB has also replaced 6,000 scupper holes/drain inlets at flood prone areas and hotspots with an improved design of Drop Inlet Chambers (DICs). Scupper holes are semi-circular holes located on the side of the road, next to the kerb, that channel stormwater into the drain. The vertical gratings in the modified DICs provide an additional vertical opening that will enable rainwater to be drained from the roads should the main horizontal gratings be partially blocked. DICs can at times be partially blocked by leaves and other debris washed down by heavy rain.
PUB has in place a network of 136 closed circuit television (CCTV) camera feeds for realtime monitoring of road conditions, which is part of PUB's flood monitoring efforts. The CCTVs are installed mostly at low-lying areas and hotspots, enabling the public to assess road conditions during storm events.
49 CCTVs are now available for public viewing, up from just 24 CCTVs when the system was first made available for public viewing in March 2012. The CCTV images are refreshed every five minutes and include new locations like Chai Chee Road and Newton Circus. The public can view these CCTV images on PUB's website or via PUB's mobile app "MyWaters". PUB will continually review the need to make more CCTV images available to the public for critical locations.
PUB will also be increasing the number of water level sensors from 158 to 198 by the end of 2014. Locations are extended to places such as Macpherson Rd/ Harvey Rd, Cambridge Rd and Thomson Rd/ Novena Rise for enhanced coverage. These water level sensors sited in the drains and canals enhance the monitoring of real-time site conditions during heavy storms and enable quick response. Information from these water level sensors is also available for public viewing. The information is updated at an interval of 10 minutes, and the public can subscribe to the SMS alert system to get updates on rising water levels in the drains or canals.
Recognising the impact of greater weather uncertainties on drainage management, PUB has revamped its drainage management approach to strengthen Singapore's flood resilience.
This "source-pathway-receptor" approach looks at catchment-wide solutions to achieve higher drainage and flood protection standards. This holistic approach covers the entire drainage system, addressing not just the pathway over which the rainwater travels (i.e. "Pathway" solutions), but also controlling rainwater at where it falls onto the ground (i.e. "Source" solutions) and at the areas where floods may occur (i.e. "Receptor" solutions).
In 2011, to strengthen "pathway" solutions, PUB raised design standards for new drains to cater for more intense extreme rainfall events. Depending on the size of the catchment, this could vary from between 15% to 50% increase in drainage capacity.
In June 2013, PUB further included a new requirement for developers to implement "source solutions" to slow down surface runoff and reduce peak flow of stormwater into the public drainage system. These on-site measures could include detention tanks and/or ABC Waters design features which will help introduce more flexibility within the existing drainage system to meet the challenges of more intense rainfall.
"Source" solutions like rain gardens have since been implemented at Livia Condominium. while at Boon Lay Meadow, a HDB development, runoff is detained in mini tanks and used for irrigation of the community garden.
In 2011, PUB also raised the minimum height of platform, land reclamation and crest protection levels for new developments and redevelopment sites under its revised Code of Practice on Surface Water Drainage. These "Receptor" measures provide additional flood protection for buildings and key infrastructure.